Lens power loss and low ambient illuminance myopia in chicks

Purpose To examine the effect of ambient illumination on lens power during the development of low light myopia in chicken eyes. Methods Chickens were reared with unrestricted vision with fluorescent lights at three illuminance levels ( 10,000 , 500 and 50 lux , respectively). Chicks were examined for refractive error, keratometry and ultrasound biometry under general anesthesia at days 30 , 60 and 90 after hatching. Lens power was calculated with a customized, previously validated, version of Bennett’s equation. Means of the ocular parameters for several age and illuminance groups were studied with repeated-measures ANOVA. Results During this three-month growth period, the refractive error of the high-illuminance group remained hyperopic, while the medium-illuminance group reached emmetropia, and the low-illuminance group developed mild myopia. For the medium- and the high- illuminance groups, this process was accompanied by an increase in axial length ( AL ) growth while the refractive power of the eye was declining in corneal and lens power. The low-illuminance group showed atypical behavior in their lens power loss. In the first phase, between Days 30–60 , their lens had the highest decrease in power, while between Days 60–90 , the lens power remained relatively stable. The increased axial elongation rate, accompanied by stable lens power, was responsible for the development of myopia in chickens reared under 50 lux . Conclusions The development of myopia in chickens raised under low ambient illuminance over 90 days may be attributed to the stability of lens power during the third month of accelerated eye growth.